50. METALLURGY OP IRON' AND STEEL.
It is stated by high, authority that carbon -deposition cannot take place without oxidation of metallic iron, by carbonic acid (C02), or by carbonic oxide according to the relation (10) or (11),
(11) 2 Fe+C02=2 FeO+C,
. ... , . . . . . .
but it is difficult to understand how these reactions can take place} in the upper zone of the blast furnace, since at the temperatures existing the reactions (1) and (9) are the only ones possible, and no metallic iron c'an exist except through reaction (9), which calls for ..carbon deposition, and this reaction, produces1 • metallic iron'( instead of oxidizing it. It may be true that at higher temperatures-the great bulk of carbon deposit is dependent -upon, or at least :ia. associated with, an oxidation of metallic iron by carbonic acid. (C02) or. carbxmie oxide (GO), but the testimony indicates that the first of the carbon deposit is formed where the temperature 'is, insufficient for- the formation of metallic iron -save by the simultaneous formation of impregnating carbon. Moreover, if metallic, iron were formed., it- could -not be oxidized -by carbonic acid (Q02), since reaction: (12) does not begin until a temperature of 300° 0;
(12) Fe+G02=FeO-f GO. : ' '
(510° F.) is reached and does not become rapiti until a still higher altitude is attained. ..',,''
On the other' hand, carbon deposition does not take place w;tli rapidity until the. temperature is. from 400° C. to 500° JO. .(say 840° F.), and this indicates that such deposition might d1epe|idi upon reaction (12) between metallic iron and carbonic aciii .(CO^)," but it may also depend upon the reduction of iron oxide by ,carb'dn, as in reactions (4)-, (5) and (6). These are all endothe:rr|iic-—i,ei^ they absorb heat, while the reduction of iron oxide by carbonic qx-1 ide (CO) 'is exothermic — i.e., it creates heat. Reaction (4) begins to take place at about 400° C. (750° F.), so that at this tempefa-J ture a supply of metallic iron is provided, and since carbonic acid (C02) is able, at this point, to oxidize metallic iron according to' reaction (12)/;there may 'coexist .all the factors necessary for any